BACKGROUND: In 2004, the U.S. Preventive Services Task Force strongly recommended that clinicians screen all pregnant women for syphilis infection. PURPOSE: To update the evidence on screening pregnant women for syphilis infection. DATA SOURCES: MEDLINE searches from 1 January 2003 through 31 July 2008, recent systematic reviews, reference lists of retrieved articles, and expert suggestions. STUDY SELECTION: English-language studies were selected to answer the following 2 questions: Does screening for syphilis in pregnancy reduce the prevalence of congenital syphilis in neonates? Are there harms of screening for syphilis or harms of treatment with penicillin in pregnancy to women or neonates? Randomized, controlled trials; meta-analyses; systematic reviews; cohort studies; and ecologic studies were selected for the potential benefits question. Randomized, controlled trials; meta-analyses; systematic reviews; cohort studies; case-control studies; and large case series were selected for the potential harms question. DATA EXTRACTION: Information on the study design, selection criteria, demographic characteristics, and clinical outcomes was extracted from each study. DATA SYNTHESIS: One study on benefits evaluated the effect before and after the implementation of a universal syphilis screening program for pregnant women and found reductions in rates of congenital syphilis. Two studies on screening accuracy for syphilis reported false-positive rates of less than 1%. One study that used a large insurance claims database reported an incidence of anaphylaxis after oral penicillin of 0.1 per 10,000 dispensings. In a study from Hungary, oral penicillin in pregnancy was not associated with orofacial clefts. LIMITATIONS: This was a targeted literature search and could have missed small studies on the benefits and harms of screening for syphilis in pregnancy. We did not review evidence on interventions to improve rates of prenatal screening. CONCLUSION: New evidence from a study of universal screening supports previous evidence on the effectiveness of screening for syphilis in pregnancy to prevent congenital syphilis. Harms include testing and follow-up for false-positive test results and adverse effects from penicillin treatment.